1、创建和使用类
使用类几乎可以模拟任何东西。
1.1创建Dog类
根据Dog类创建的每个实例都将存储名字和年龄。我们赋予了每条小狗蹲下sit（）和打滚roll_over()的能力
#!/usr/bin/env python
class Dog:
"""一次模拟小狗的简单尝试"""
def __init__(self,name,age):
"""初始化属性name和age"""
self.name = name
self.age = age
def sit(self):
"""模拟小狗被命令时蹲下"""
print(self.name.title() + " is now sitting!")
def roll_over(self):
"""模拟小狗被命令时打滚"""
print(self.name.title() + "roll over!")
my_dog = Dog('white',18)
print("My dog name is " + my_dog.name.title() + ".")
print("My dog is " +str(my_dog.age) + " years old!")
my_dog.sit()
my_dog.roll_over()
================================================
My dog name is White.
My dog is 18 years old!
White is now sitting!
Whiteroll over!
1.2创建多个实例
#!/usr/bin/env python
class Dog:
"""一次模拟小狗的简单尝试"""
def __init__(self,name,age):
"""初始化属性name和age"""
self.name = name
self.age = age
def sit(self):
"""模拟小狗被命令时蹲下"""
print(self.name.title() + " is now sitting!")
def roll_over(self):
"""模拟小狗被命令时打滚"""
print(self.name.title() + "roll over!")
my_dog = Dog('white',18)
your_dog = Dog('black',19)
my_dog.sit()
my_dog.roll_over()
your_dog.sit()
your_dog.roll_over()
==============================================
White is now sitting!
Whiteroll over!
Black is now sitting!
Blackroll over!
2、使用类和实例
①Car类
#!/usr/bin/env python
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = year
def get_descriptive_name(self):
"""返回整洁的描述信息"""
long_name = str(self.year) + ' ' +self.make + ' ' + self.model
return long_name.title()
my_new_car = Car('audi','a4',2017)
print(my_new_car.get_descriptive_name())
===============================================
2017 Audi A4
②给属性指定默认值
#!/usr/bin/env python
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述信息"""
long_name = str(self.year) + ' ' +self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
print("This car has " +str(self.odometer_reading) + " miles on it.")
my_new_car = Car('audi','a4',2017)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
============================================
2017 Audi A4
This car has 0 miles on it.
③修改属性的值
可以以三种不同的方式修改属性的值：直接通过实例进行修改；通过方法进行设置；通过方法进行递增（增加特定的值）
- 直接修改属性的值
#!/usr/bin/env python
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 23
def get_descriptive_name(self):
"""返回整洁的描述信息"""
long_name = str(self.year) + ' ' +self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
print("This car has " +str(self.odometer_reading) + " miles on it.")
my_new_car = Car('audi','a4',2017)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
===============================================
2017 Audi A4
This car has 23 miles on it.
- 通过方法修改属性的值
#!/usr/bin/env python
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述信息"""
long_name = str(self.year) + ' ' +self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
print("This car has " +str(self.odometer_reading) + " miles on it.")
def update_odometer(self,mileage):
"""将里程表读数设置为指定的值"""
self.odometer_reading = mileage
my_new_car = Car('audi','a4',2017)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23)
my_new_car.read_odometer()
==============================================
2017 Audi A4
This car has 23 miles on it.
对Car类所做的唯一修改是添加了方法update_odometer()。这个方法接受一个里程值，并将其存储到self.odometer_reading中。
3、继承
编写类时，并非总是从空白开始。如果你要编写的类时另一个现成类的特殊版本，可使用继承。一个类继承另一个类时，它将自动获得另一个类的所有属性和方法；原有的类称为父类，而新类称为子类。子类继承了其父类的所有属性和方法，同时还可以定义自己的属性和方法。
#!/usr/bin/env python
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""返回整洁的描述信息"""
long_name = str(self.year) + ' ' +self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的信息"""
print("This car has " +str(self.odometer_reading) + " miles on it.")
def update_odometer(self,mileage):
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You cant roll back an odometer!")
def increment_odometer(self,miles):
self.odometer_reading += miles
class ElectricCar(Car):
"""电动车的独特之处"""
def __init__(self,make,model,year):
"""初始化父辈的属性"""
super().__init__(make,model,year)
my_tesla = ElectricCar('tesla','model s',2017)
print(my_tesla.get_descriptive_name())
==========================================
2017 Tesla Model S
4、导入类
#!/usr/bin/env python
from car import Car
my_new_car = Car('audi','a4',2017)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
=======================================
2017 Audi A4
This car has 23 miles on it.
从一个模块中导入多个类：
from car import Car,ElectricCar